Breathing Mechanics (Quiet, Forced, Speech)

(Quiet Breathing) What is the goal of quiet breathing?

• Gas exchange → CO₂ (carbon dioxide) for O₂ (oxygen)

(Quiet Breathing) What is alveolar pressure at baseline?

• Alveolar Pressure = Atmospheric Pressure

(Quiet Breathing) What occurs during active inspiration?

• Diaphragm contracts & flattens

• Intercostal elevate & twist ribs

• Thorax expands

  • Intra-pleural pressure (pressure in the lungs) decreases

• Abdomen compresses

  • abdominal pressure increases

• Further thoracic expansion

  • Intra-pleural pressure decreases some more

  • Alveolar pressure decreases

• Lungs pulled by chest wall – alveoli expand

• Alveoli expansion is passive

(Quiet Breathing) How does lung pressure change with decreased alveoli pressure?

• lung pressure is now less than atmospheric pressure, & air enters the system

• Air continues to enter until baseline pressures (alveolar = atomospheric)

(Quiet Breathing) What occurs during expiration (exhalation)?

• Passive expiratory forces = relaxation pressures

• Gravity

• Torque

• Elastic recoil

• all work together to reverse actions of inspiration!

(Quiet Breathing) How do intrapleural & alveolar pressures change during expiration?

• Both intrapleural pressure and alveolar pressure are greater than atmospheric pressure.

What is the gas exchange process?

• CO₂ for O₂

• exchange is via the alveolar capillaries

  • “dead space” – structures of no gas exchange

  • Walls too thick so not O₂ permeable

• O₂ carried via Hemoglobin (Hb)

What is the process of gas exchange at alveoli?

• respiration!

What is the process of gas exchange in/out of lungs?

• ventilation!

(Gas Exchange Process) What is the respiratory rate for a normal adult?

• 12-20 breaths per minute (bpm)

(Gas Exchange Terms) Oxygen Saturation:

• amount of oxygen in the blood

  • SpO₂ = measured peripherally w/ a sensor (“pulse oximetry”)

  • SaO₂ = measured internally in the lab thru blood

(Gas Exchange Terms) Perfusion:

• amount of blood (& therefore oxygen) reaching the tissue

(Gas Exchange Terms) Hypoxemia:

• Not enough O₂ in the blood

(Gas Exchange Terms) Hypoxia:

• Not enough O₂ in the tissue

(Gas Exchange Terms) Hypercapnia:

• excessive CO₂ in the blood

Forced Breathing:

• body has increased demand for air

  • during physical exertion (healthy person)

(Forced Breathing) What does forced inhalation require?

• use of primary AND accessory muscles of respiration

(Forced Breathing) What does forced exhalation require?

• passive expiration AND active contraction of intercostals & abdominal muscles

(Forced Breathing) What occurs to tidal volume during forced breathing?

• it increases

(Forced Breathing) Respiratory rate?

• stays the same or slows down

What does speech breathing require?

• active inspiration AND active expiration against/through:

  • upper airway resistance

  • continuously modulating due to VF & articulator valving action

Inspiration during speech breathing:

• cycle is shorter relative to expiration

When does phonation occur?

• on expiration

Should speech breathing require larger inspiratory volumes?

• Should not require larger inspiratory volumes—typically, if adequate breath support for quiet breathing exists, then, adequate breath support for speech exists,

  – But:

  • Louder voice requires increased inspiratory volume above tidal volume

  • Longer phrases require increased inspiratory volume above tidal volume

What is tidal volume at during speech breathing?

• ~35-40% of vital capacity

• Conversation = initiated w/ large increase in air up to ~55-60% of vital capacity

So, speech breathing really uses some amount of inspiratory reserve volume or “extra air”

• ~20% more than tidal volume ?

Speech breathing requires more air than regular quiet breathing (tidal breathing), because you need to produce longer and more controlled exhalations to speak in phrases or sentences.

• Tidal volume (TV) is the amount of air you breathe in and out at rest.

• When speaking, you typically inhale about 20% more air than tidal volume, tapping into your inspiratory reserve volume (IRV)—the “extra air” you can inhale beyond a normal breath.

Key Point:

Speech breathing uses ~20% more air than tidal breathing by drawing from inspiratory reserve volume to support longer, controlled exhalation needed for speech.

What is required to maintain adequate alveolar pressures for speech (& life)?

• Balance between active inhalation, active exhalation, and passive exhalation/recoil

(Neurophysiology of Breathing) What is the role of the Brainstem Central Pattern Generator (CPG)?

• maintains balanced O₂ & CO₂

• CO₂ levels are the primary drivers of ventilation regulation

What are the 2 main types of receptors for breathing?

• chemoreceptors

• stretch receptors

Chemoreceptors (blood-bourne):

• react to the amount of a chemical in the system

  • Central

  • Peripheral

(Chemoreceptors) Central:

• in the medulla (anatomically separated from the respiratory CPG); react to chemistry changes in CSF

  • CO₂ → receptors constantly monitoring levels and adjusting ventilation as need to keep acid (H+) /base (HCO₃^-) balanced (respiratory homeostasis)

(Chemoreceptors) Peripheral:

• CO₂ receptors—in the aortic body & in the carotid bodies, constantly monitoring & adjusting to keep homeostasis, sends info to the medulla

• »  O₂ receptors –in the aortic body and carotid bodies; while constantly monitoring, only react when levels are low.

Stretch receptors (afferent & efferent neural):

• React to the amount of muscle stretch in a muscle system

  • Breathing—in the smooth muscle of the airway, react to expansion/deflation of the lungs and bronchi

(Blood Gases) What does respiration work with to regulate CO₂ in the system (blood)?

• renal function!

• Respiration: CO₂ exhaled

• Renal: HCO₃ exreted out through kidneys/bladder

What can occur if there is a problem in either respiration or metabolic renal function?

• the body loses homeostasis, pH will either rise or fall depending

  • pH high = alkalosis

  • pH low = acidosis

Hyperventilation:

• excessive ventilation, lungs eliminate more CO2 than is produced, so there is not enough left in the blood

  • → Respiratory Alkalosis (pH high)

Hypoventilation:

• inadequate ventilation, lungs don’t eliminate enough CO2 so body retains CO2

• → Respiratory Acidosis (pH low)